The present invention relates to the nuclear medicine art. It finds particular application in conjunction with multiple detector single photon emission computed tomography (SPECT) camera systems and will be described with particular reference thereto.
Early nuclear or Anger cameras had a single radiation detector head which was positioned stationarily over a region of interest of the subject. The subject was injected with a radioactive dye which circulated through the patient's circulatory system. Some of the radiation given off by the dye was received by the gamma camera detector head which converted the radiation event into light.
More specifically, the detector head included a scintillation plate which converted each received radiation event into a scintillation or flash of light. An array of photomultiplier tubes positioned in the back of the scintillator plate and associated circuitry determined an (x,y) coordinate location and an energy of (z) value for each scintillation event. A collimator including a grid-like array of lead vanes limited the path or trajectory of radiation events which could strike the scintillation plate. Typically, the collimator constrained each incremental element of the scintillator plate to be receptive only to radiation directly in front of it, i.e., radiation along paths substantially perpendicular to the scintillator plate. The collimator must be positioned as close to the patient as possible to acquire image data required to generate high resolution images. In this manner, a shadowgraphic image of the frequency of radiation events in the examined region of the subject was developed.
In SPECT imaging, the detector is rotated around the subject or indexed to a multiplicity of angularly offset positions around the subject to collect a data which is the mathematical equivalent of a CT scanner data set. More accurately, because the nuclear camera head is two-dimensional, a series of data sets are collected, each corresponding to one slice of an imaged volume.
Instead of a single detector head, other gamma cameras have two detector heads positioned on opposite sides of the subject. Placing two detector heads in this manner improves the resolution and data collection efficiency, particularly for whole body imaging. For other studies, particularly cardiac studies, it is advantageous to position the detector heads orthogonally to each other. This enables a complete 180 degree data set to be collected by rotating the pair of detector heads only 90 degrees relative to the subject. Still other gamma cameras have three heads placed at 120 degree intervals around the subject. Typically, the heads are movable radially toward and away from the patient and the three heads are rotatable, as a unit, around the patient. In each case, the detector face is placed as close as possible to the patient during.
Each of the foregoing systems has various advantages and disadvantages. The cost of a gamma camera system increases as additional detector heads are added. Systems having two opposed detector heads are particularly useful for whole-body imaging. Wide field of view detectors, which permit scanning of the entire width of the body, are preferably used in this application. Systems having two orthogonal detectors are commonly used for cardiac imaging. Because a wide field of view is not required in cardiac applications, smaller detectors are preferably used to allow the detectors to be placed as close as possible to the patient. Three detector head systems are often used in connection with high resolution brain and cardiac imaging. Although wide field of view detectors are desirable for body imaging, their physical size again limits performance in head imaging. The placement of the three detector heads also limits the utility of three detector systems in whole body and brain applications.
These tradeoffs limit the versatility of traditional gamma camera systems. As a result, various attempts have been made to address them.
U.S. Pat. No. 5,444,252 to Hug, et al., issued Aug. 22, 1995 discloses a two detector system whereby the detectors are transformable between opposed and orthogonal positions. A separate driven mechanism and ring gear for each of the detectors increases the cost and physical complexity of the system. The minimum distance between the detectors and the patient in the orthogonal configuration, and hence system performance, is also limited by the physical size of the detector heads.
Co-pending U.S. application Ser. No. 08/292,785 now U.S. Pat. No. 5,569,924 discloses a system having two detectors which can be transformed between opposed and orthogonal configurations. Although the physical size of the detectors continues to limit the minimum distance between the patient and the detectors in the orthogonal configuration, this effect is reduced by offsetting the detector field of view from the center of rotation. This system is not readily adapted to a three detector configuration, however.
Co-pending U.S. application Ser. No. 08/635,390 now U.S. Pat. No. 5,717,212 discloses a three detector system where two of the three heads can be independently positioned about the gantry so that 120 degree three head, 180 degree opposed, and 90 degree orthogonal configurations can all be achieved. Although the physical size of the detector again limits the minimum distance between the detectors and the patient, the distance is reduced in the 90 degree orthogonal position by varying the angle from 90 degrees. The physical size of the detectors again limits the minimum distance between the detector faces and the patient in the 120 degree configuration.
The present invention provides a gamma camera which addresses the above-referenced shortcomings, and others.